Our major aim is to obtain new information about bacteriophage and bacterial DNA replication. Such studies are fundamental to the eventual understanding of DNA function in normal and abnormal growth, virus behavior and mutagenesis. Our studies utilize physical, biochemical and genetic techniques with major emphasis on physicochemical and electron microscopic methodology. We wish to determine why some replicators employ a bidirectional mode of DNA replication, other replicate unidirectionally and yet others switch their mode of replication. What evolutionary pressures favored these various strategies for DNA duplication? The segment of DNA that is responsible for the initiation of DNA replication will be studied in greater detail. We wish to find out exactly what properties this very important sequence has to have in order to be functionally active. Can other sequences take on such a function under unusual conditions? Minor aims are to continue studies on DNA helical stability. We wish to have more accurate understanding of the magnitude of effects produced by A+T or G+C rich segments on neighboring DNA sequences. Studies will also be continued on learning more about internal structure of bacteriophage. Our investigations will rely heavily on electron microscopic methods and to this end we wish to develop new techniques in this area and to extend the usefulness of electron microscopic partial denaturation mapping. One technique of immediate interest is development of a system capable of automatic DNA length measurement.